The present invention relates to an electrothermic non-impact recording material, and more particularly to an electrothermic non-impact image transfer recording material for use with noiseless typewriters, computer output apparatus or facsimile apparatus.
In accordance with the remarkable development of the performance of computers and facsimile apparatus, printers which serve as the terminal apparatus thereof have become important apparatus. The printers for use with computers and facsimile apparatus can be roughly classified into two categories, an impact-type printing system (i.e., a mechanical printer) and a non-impact-type printing system. As the recording system which belong to the non-impact-type printing system, the following five systems are known: (1) electrophotographic recording system, (2) thermosensitive recording system, (3) electrical discharge recording system, (4) thermosensitive image transfer recording system and (5) electrothermic image transfer recording system.
The first mentioned impact-type printer has the shortcoming that it generates noise during operation because of its mechanical structure, and this shortcoming cannot be avoided.
The non-impact-type recording system has the advantage that it does not generate noise during operation, but it has several problems as well. For instance, in the electrophotographic recording system, a complex process comprising five steps, charging, exposure, development, image transfer and cleaning, is required, and this system is still unreliable in obtaining good quality transferred images. Furthermore, it is difficult to produce a small-size apparatus using the electrophotographic recording process.
The thermosensitive recording system has the shortcoming that the preservability of a thermosensitive recording material for use in that system has not been improved enough for practical use. Further, it has the shortcoming that the thermosensitive recording material cannot be plain paper, but it is made of processed paper.
The electrical discharge recording system has the advantage that image transfer can be performed to plain paper by electrical discharge, but it has the shortcoming that unpleasant odor comes out or burning dust is produced by the electrical discharging.
The thermosensitive image transfer system has the shortcoming that images with high resolution cannot be obtained because of the use of a thermal head when printing. The maximum image resolution that is obtained at present is in fact about 10 lines/mm. Further, this sytem has the shortcoming that the recording speed is as slow as about 1 msec/dot.
Unlike the above-mentioned non-impact-type printing system, the electrothermic non-impact-recording system has the advantages that images with high resolution can be obtained on plain paper with high recording speed, and the apparatus for this system can be made compact in size. Due to such advantages thereof, several proposals have been made for further improvement of electrothermic non-impact recording materials for use with this system.
For example, in Japanese Laid-Open patent application No. 54-87234, there is proposed an electrothermic non-impact recording material comprising an electroconductive support material and an image transfer layer formed thereon, which image transfer layer comprises as the main components a colorant and a thermoplastic polymeric resin which is soluble in a solvent, by which solvent the support material is not damaged even if it comes into contact with the solvent, and which thermoplastic polymeric resin has a softening point lower than that of the support material. In this electrothermic non-impact recording material, it is preferable that the support material which serves as a base layer be made of a polycarbonate resin with electroconductive carbon black particles dispersed therein. In the electrothermic non-impact recording material disclosed in this patent application, the image transfer layer which serves as an ink layer has excellent resistance to friction, but its mechanical strength is not enough for practical use, which is a shortcoming of this recording material.
In Japanese Patent Publication No. 55-12394, Japanese Laid-Open patent application No. 53-7246, Japanese Laid-Open patent application No. 56-8276 and Japanese Patent Publication No. 55-12393, there are proposed two-layered type electrothermic non-impact recording materials, each comprising an anisotropically electroconductive base layer or a metal-powder-dispersed electroconductive base layer, and an electroconductive ink layer formed thereon. The anisotropically electroconductive base layer is expensive since it is produced by a complex production method by use of expensive materials, such as metal powder. In the case of the metal-powder-dispersed electroconductive base layer, it is extremely difficult to disperse the metal powder uniformly in the layer. Therefore, the electrothermic non-impact recording materials disclosed in the above patent publications and applications have the shortcoming that high resolution cannot be obtained because of the non-uniformity of the dispersion of the metal powder in the base layer by which non-uniformity printed dots are deformed.
In other conventional electrothermic image transfer recording materials, the layer which comes into contact with the recording styli of recording electrodes does not have sufficient resistance to heat and mechanical strength, so that the layer is easily damaged by the heat necessary for forming images with high dot density, and the recording styli are easily smeared by the materials coming from the layer. By these shortcomings, high dot-image density, which could be obtained by application of high voltage and large electric current, cannot be obtained. In contrast to this, if the thermal resistance of the layer is improved in the conventional electrothermic image transfer recording materials, the flexibility necessary for practical use thereof is lost and they become easily torn, with the result that it is difficult to perform smooth scanning of the recording styli on the recording materials.
A conventional electrothermic recording material composed of a plurality of layers has the shortcoming that part of the base layer is transferred together with the ink layer in the image transfer step, resulting in that the density and shape of printed dots become non-uniform and the quality of the dot images is inferior to that obtained by the conventional single-layer-type electrothermic image transfer recording materials.
As mentioned above, in the conventional electrothermic image transfer recording materials, since the mechanical strength of the layer which comes into contact with the recording styli is insufficient, the utmost care has to be taken when producing, loading in cartridges or transporting the recording materials.